P. N. Gajjar

THE STUDY OF SUPERCONDUCTING STATE PARAMETERS OF in-BASED BINARY ALLOYS BY PSEUDOPOTENTIAL

The study of the superconducting state parameters (SSP) viz. electron–phonon coupling strength λ, Coulomb pseudopotential μ*, transition temperature TC, isotope effect exponent α and effective interaction strength N0V of In-based binary alloys In1-xNax, In1-xMgx, In1-xZnx, In1-xTlx, In1-xSnx, In1-xPbx and In1-xBix have been made extensively in the present work using a model potential. To explain electron–ion interaction pseudo-alloy-atom (PAA) model is applied for the first time instead of Vegards Law. A considerable influence of various exchange and correlation functions on λ and μ* is found from the present study. It is also concluded that TC strongly depends on the value of the effective valence Z* of binary alloys.

Total energy, equation of state and bulk modulus of AlP, AlAs and AlSb semiconductors

Recently proposed model potential which combines both linear and quadratic types of interactions is employed for the investigation of some properties like the total energy, equation of state and bulk modulus of AlP, AlAs and AlSb semiconductor compounds using higher-order perturbation theory. The model potential parameter is determined using zero pressure condition. The ratio of the covalent bonding termEcov to the secondorder termE2 is 6.77% to 11.85% which shows that contribution from higher order terms are important for zinc-blende-type crystals. The calculated numerical results of the total energy, energy band gap at Jones-zone face and bulk modulus of these compounds are in good agreement with the experimental data and found much better than other such theoretical findings. We have also studied pressure-volume relations of these compounds. The present study is carried out using six different screening functions along with latest screening function proposed by Sarkaret al. It is found from the present study that effect of exchange and correlation is clearly distinguishable.

Asphericity in the Fermi Surface and Fermi Energy of Na－K,Na－Rb and Na－Cs Binary Alloys

Detailed theoretical investigations into asphericity in the Fermi surface (FS) and Fermi energy (FE) ofNa1_xKx, Na1_xRbx, and Na1_xCsx binary solid solutions are carried out for the first time. The alloying behavior ofthe K, Rb, and Cs with the Na generates the Fermi surface distortion (FSD) of bce simple metals. The FS of Na-K,Na-Rb, and Na-Cs solid solution is a distorted sphere with the largest deviation along [110]. We have found that theimpact of local-field correction function on FSD is maximun at [100] point and minimum at [111] point. The exchangeand correlation effect is found to suppress the value of FE.

Fermi energy and Fermi surface distortion of the Cs–K, Cs–Rb and Rb–K binary systems

Abstract Systematic theoretical investigation of the Fermi energy (FE) and the Fermi surface distortion (FSD) of Cs0.7Rb0.3, Cs0.3Rb0.7, Cs0.7K0.3, Cs0.3K0.7, Rb0.71K0.29 and Rb0.3K0.7 disordered alloys have been reported for the first time by using the pseudo-alloy-atom model. A local pseudopotential consisting of a Coulombic term outside the core and varying cancellation of interaction within the core is proposed to describe the electron–ion interaction in each of these systems. The influence of various local-field correction functions on the aforesaid properties is 64–93%. The distortion of the Fermi surface (FS) along major symmetry directions obeys the metallic behavior. For the Cs1−xRbx and Cs1−xKx systems, the FSD along the zone boundaries increases with the atomic volume. For Rb1−xKx, a reverse trend is observed. The maximum anisotropy in the FS for the six binaries is observed at the [1xa01xa00] point.

Some static and vibrational properties of aluminium by a local pseudopotential

The pseudopotential investigation of various properties of aluminium is studied in terms of the real-space sum of Born-von Karman central-force constants. A simple local model potential depending on a single parameter has been used to investigate the ion-ion interaction, interatomic force constants, dynamical elastic constants, bulk modulus, deviation from Cauchy relation, Poissons ratio, Youngs modulus, propagation velocity of elastic waves, phonon dispersion curves and degree of elastic anisotropy. The effect of exchange and correlation on conduction electrons is also considered separately by using various forms of the dielectric (screening) functions. Overall good agreement with the available theoretical and experimental data is achieved in the present work.

Collective modes in Ca70Mg30 glass

The self-consistent phonon scheme given by Takeno and Goda, involving multiple scattering and phonon eigen frequencies which are expressed in terms of many-body correlation functions of atoms as well as of interatomic potential in the solids, has been used to generate the collective modes in the Ca70Mg30 glass. A model potential is proposed to describe the effective interaction in the glass. Three different forms of the local field correction functions viz. Hartree, Taylor and Ichimaru and Utsumi are used to examine relative influence of exchange and correlation effects. The phonon frequencies of the longitudinal and transverse modes are computed employing the theoretical formulation of Hubbard and Beeby. The elastic property of the glassy system is then studied using the long wavelength limits of the phonon modes. The theoretical computations reproduce much better dispersion curves (both for the longitudinal and transverse phonons) compared to earlier reports and are found to be in good agreement with the available experimental results due to neutron scattering.

Thermodynamic properties of liquid alkali metals

The internal energy, entropy and Helmholtz free energy of liquid alkali metals, viz. Na, K, Rb and Cs are investigated using pseudopotential perturbation scheme based on Gibbs-Bogoliubov variational technique. A local pseudopotential is applied to describe the electron-ion interaction in the liquid alkali metals. To introduce the exchange and correlation effects, the local field correction function proposed by Taylor is employed. The computed values for internal energy, entropy and Helmholtz free energy for the liquid alkali metals are in excellent agreement with the experimental data.

Asphericity in the Fermi surface of aluminium and lead

A detailed study of asphericity in the Fermi surface of aluminium (Al) and lead (Pb) along three symmetry directions [100], [110] and [111] is made on the basis of pseudopotential theory extending upto second order. The influence of exchange and correlation effects on the asphericity in the Fermi surface is examined explicitly by using four different forms of screening function. For polyvalent metals Al and Pb the distortion in the Fermi surface is found to be sensitive in regard to various local field corrections.

STRUCTURAL STUDY OF LIQUID RARE EARTH METALS FROM CHARGED HARD SPHERE REFERENCE FLUID

The present article deals with the investigation of structure factor, s(q) ; radial distribution function, g(r) and interatomic distance, r1 of liquid rare earth metals, Nd, Dy, Ho, Er and Lu by adopting Charged Hard Sphere (CHS) reference fluid. To describe electron-ion interaction, our well established model potential along with the dielectric function due to Taylor is used. Good agreement between present and experimental findings is concluded.

Structure and collective dynamics of liquid sodium

The temperature variation of the longitudinal and transverse phonon frequencies of liquid sodium is investigated using the approach by Hubbard Beeby. The molecular dynamics simulation is used to generate the pair correlation function of liquid sodium at various temperatures viz. T = 378 K, 473 K, 573 K, and 723 K, with 672 particles. To describe the electron-ion interaction our own model potential is employed along with a recent local field correction function due to Sarkar et al. To evaluate the parameter of the potential the zero pressure condition has been applied. The present results of g(r) are in good agreement with available experimental findings. The computed g(r) are used to investigate the temperature variation of the collective dynamics of liquid sodium. The amplitudes of the peaks of the longitudinal and transverse frequencies are suppressed while the width of the propagation gap for the transverse sound waves decreases with an increase in temperature. The computed longitudinal and transverse sound velocities at these temperatures are found to be